The goal of this effort is to develop an advanced laser lithotripter for the treatment of kidney stones. The proposed approach is based on exploiting alexandrite lasers, a newly emergent solid state laser technology that offers a unique combination of properties potentially important for the development of reliable and inexpensive protocols which can be routinely applied in small clinics and doctors' offices as well as in large research hospitals. These laser properties include: small size, high reliability, variable pulse duration and power, high pulse energy, and a wavelength benign to normal bladder and uretal tissues and compatible with small diameter optical fibers. The Phase I effort is aimed at demonstrating effectiveness of the proposed lithotripter in in vitro and in vivo testing using a variety of stone compositions and fiber optic delivery systems. Optimum laser and fiber delivery parameters for stone fragmentation will be determined. Phase 11 will continue in vivo testing with refined models and procedures. It will result in the development of a commercial lithotripter prototype suitable for human clinical studies and in the development of protocols and procedures for such studies. It is anticipated that this work could lead directly to less expensive and more widespread application of laser lithotripsy.